Colossal etailer Amazon is going to buy its corporate headquarters in Seattle for $1.16bn, according to a company filing.

The internet giant told the Securities and Exchange Commission that it's planning to snap up the complex of 11 buildings, around 1.8m square feet of office space, by the end of this year. The property is currently owned by the investment firm of Microsoft co-founder Paul Allen.

The deal will be the most expensive purchase anywhere in the US of a single office property, real estate beancounters at Real Capital Analytics said. Amazon will be forking out $644 per square foot, more than double the average rate of $308 in the city, Reuters reported.

The etailing HQ is located in South Lake Union, the trendy centre for tech firms in Seattle.

Allen's Vulcan Real Estate, part of his Vulcan investment firm, put the buildings up for sale in August. Amazon had been leasing the HQ from Vulcan.

The company has already put down a non-refundable deposit of around $23m, which will go up to $51m in a couple of weeks. Amazon is hoping to close the sale by the end of the year and the deposit will be forfeit if it doesn't. ®